The development of digital computers has created a need for devices which can convert information found in analog form such as maps, graphs and models to digital data so that the information can be processed by the computer.
Several devices are currently used to digitize two dimensional forms. Typically these devices has a stylus, cursor, index or other structure for defining data points. Such a structure is collectively referred to herein as a stylus and is moved to spaced points on the form. The computer senses the position of this stylus and converts digital data representing the sensed position to appropriate Cartesian, polar or other coordinate system data. A plurality of such data points then define the form in digital format.
One conventional type of digitizer uses a specially constructed table or tablet upon which the form to be digitized is mounted. For example, the device of U.S. Pat. No. 3,732,557 utilizes a conductor array in the tablet. U.S. Pat. No. 3,792,243 discloses a capacitance tablet. The principal difficulty with such tablet dependent digitizers is that the tablets are expensive to construct and the size of the form to be digitized is limited to the size of the tablet. Additionally, such tablets are not very portable and therefore can be used only in limited places.
A difficulty with tablet dependent digitizers using a matrix is that the computer must continuously scan the matrix looking for input position signals. This scanning operation takes considerable computer time and therefore requires that the stylus be moved more slowly between data points thus lengthening the time required to complete the entire job.
Still other digitizing devices use orthogonally related bars, carriages and tapes such as those shown in U.S. Pat. Nos. 3,271,562 and 2,413,300. Such devices, however, not only are similarly constrained to limited physical sizes but are complicated and bulky mechanical structures which are inconvenient and clumsy to use. The long bars on mechanical structures used in some digitizer equipment are not only difficult to use because they tend to be in the way but they have a tendency to bend and therefore cause inaccuracy.
Still other devices utilize radiant energy such as sound, light or electromagnetic energy to detect the position of the stylus. Such devices are shown in U.S. Pat. Nos. 4,138,592, 3,515,888 and 4,124,838.
There is therefore a need for a structurally simpler digitizer which is easy to use and can be fabricated at a considerably lower cost. The present invention offers these advantages and is also portable and can digitize at a faster speed. The present invention is not tablet dependent because no special tablet and in fact no tablet is necessary.
Digitizers constructed in accordance with the present invention may be mounted upon a wall, for example, to digitize a large wall mounted map. They may be transported out into the field to digitize objects or forms which can not be brought to the computer. The digitizer of the present invention has no bulky carriages or tracks which must extend over the form to be digitized.
Another feature of the present invention is that as a result of its simplicity, fewer computer operations are needed to convert input position data from the digitizer to coordinate system data.
Digitizers constructed in accordance with the present invention may be used to digitize both two-dimensional and three-dimensional forms. Two-dimensional forms, such as contour maps or transit routes may be digitized. Also, graphically presented data may be digitized. The digitizer of the present invention may be used for computer generation of graphics.
Digitizers constructed in accordance with the present invention may also be utilized to digitize three-dimensional objects. This is useful, for example, for preparation of graphics from a solid model, the plotting of graphs or the preparation of technical drawings. Further, the present invention may be used to generate data from a model or pattern for controlling a numerically controlled machine tool.